Electric spark gap



N. HENDRY ETAL 2,491,979

ELECTRIC SPARK GAP Dec. 20, 1949 Filed June 19, 1945 ATTORNEY.

Patented Dec. 20, 1949 2,491,979 ELECTRIC SPARK GAP Norman Hendry,

Ealing, London,

and J ohn Andrew Laird,v Coventry, England, assignors to Rotax Limited, London, England Application June 19, 1945, serial No. 600,345

In Great Britain June 19, 1944 s claims. (o1. 315-58) This invention relates to electric'spark gaps and particularly of the enclosed kind used in association with high-tension ignition apparatus for internal combustion engines. The object of the invention is to provide a gap of improved construction whereby the sparking voltage for a given gap-setting is -kept substantially constant.

The invention comprises the combination of a pair of massive main electrodes, a pair of small auxiliary electrodes associated with the main electrodes, one ofv which is-`connected to one of the main electrodes by a high resistance or a capacity, and a gas-tight envelope enclosing the gaps between the main and auxiliary electrodes.

In the accompanying drawing wherein like reference characters refer to like parts throughout the several views, Fig. l is a sectional side view illustrating diagrammatically an electric spark gap constructed in accordance with the invention, and Fig. 2 is a similar detail View showing a modification.

In carrying the invention into effect as shown, we employ a pair of similar main electrodes a. These electrodes each consist of a relatively massive piece of copper or other metal of good electrical and thermal conductivity, and their adjacent ends are conveniently of truncated conical form. To each of the adjacent ends of the electrodes a is secured a tip b of tungsten which is preferably in the form of a flat disc, though its outer face may be slightly convex, the two tips being separated from each other by a gap. In one of the electrodes a is formed an oblique hole c adapted to receive an element d which may be a high-resistance element of any convenient small and compact form, such as for example, carbon granules, or a fused mixture of metal and glass powder. Alternatively the element d may be replaced by a small capacity element m. The element d is insulated from the associated electrode a by an enclosing tube e of glass or any other convenient insulating material. One end of the element d is attached by a wire f or other means to the outer end of the main electrode a. in which it is mounted, ,and the other end is attached to an auxiliary electrode y in the form of a wire, the free end of which is situated adjacent to the gap between the main electrodes. Another auxiliary electrode h (which also preferably consists of a wire) is secured to or formed o 2 electrodes a, but it may be arranged on the axis oi the main gap.

The gaps between the main and auxiliary electrodes a, g, h are contained lin `a gas-tight envelope i. This may conveniently consist of "a short glass or other insulating tube y" having its ends fused or otherwise connected vto the main electrodes a, or having its ends connected tothe main electrodes by thin metal rings lc whose ends are respectively secured "(by fusion or otherwise) to the ends of the insulating tube and the main electrodes. The diameter of the envelope iis such as will provide adequate gas space around the electrodes a, g, h.

The main and auxiliary electrodes a, g, 71l are such thatl the assembly acts in the same way as a gap oi the well known three-point type, but by arranging a high resistance or a capacity in the discharge path containing the auxiliary gap, we ensure reliable and uniform action of the main gap in avery simple and convenient manner.

A gap as above described can be constructed in a small and compact form, and is particularly intended for use in high tension ignition systems where it is required to provide a gap to control the discharge of a condenser through the primary winding of a transformer, the secondary winding of which is connected to the engine sparking plug. The invention is not, however, limited to the example above described, as constructional details may be modied to suit different requirements. Thus, instead of accommodating the resistance or capacity element within one of the main electrodes, this element may be coiled around one of the main electrodes, or otherwise disposed.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. An electric spark gap comprising the combination of a pair of massive main electrodes, a pair of small auxiliary electrodes associated with the main electrodes, one of which is connected to one of the main electrodes by a high resistance, the gap between said auxiliary electrodes being shorter than the distance between either of said auxiliary electrodes and the main electrode of opposite polarity, and a gas-tight envelope enclosing the gaps between the main and auxiliary electrodes.

2. An electric spark gap comprising the combination of a pair of massive main electrodes, a pair of small auxiliary electrodes associated with the main electrodes, one of which is connected to one of the main electrodes by a small capacity and which approaches the other auxiliary electrode more closely than it does the other main electrode, and a gas-tight envelope enclosing the gaps between the main and auxiliary electrodes.

3. A spark gap adapted for use in an ignition circuit comprising a pair of massive 'electrodes arranged as a spark gap, a wire projecting from one electrode in proximity to said gap, the other electrode having a hole therein, an insulated tube in said hole including a high resistance, means at one end of said tube connecting saidY resistance to said other electrode, a wire connected with said resistance and projecting from the other end of said tube into spark gap relation with said rst-named wire, and a sealed envelope enclosing said gaps. Y

4. A spark gap adapted for use in an ignition circuit comprising a pair of massive electrodes arranged as a spark gap, a wire projecting from one electrode in proximity to said gap, the other electrode having a hole therein, an'insulated tube in said hole including a. small capacity, means at one end of said tube connecting said capacity to said other electrode, a wire connected With said capacity and projecting from the other end of said tube into spark gap relation with said first-named Wire, and a sealed envelope enclosing said gaps.

5. A spark gap adapted for use in a magneto circuit comprising a pair of massive electrodes having tips arranged as a spark gap, a wire projecting from one electrode in proximity to said gap, the other electrode having an insulated hole therein, a Wire projecting from an end of said hole into spark gap relation to said iirstnamed wire, an impedance in connection with the second wire to regulate the iiow of current across the gap between the wires, means to connect said other electrode to said regulating means, and a sealed insulating ring enclosing said gaps.

6. A spark gap adapted for use in a. magneto circuit comprising a pair of massive electrodes arranged as a spark gap, wires projecting from said electrodes in spark gap relation, one of which is connected to its electrode through an impedance constituting current controlling means, and means to enclose said gaps.

7. A spark gap adapted for use in a magneto circuit comprising a pair of massive electrodes arranged as a spark gap, and a pair of electrode points arranged as a spark gap, said electrode points being connected to said electrodes and at least one of them being so connected by an impedance constituting current controlling means.

8. A spark gap of controlled discharge comprising a pair of electrodes in spark gap relation and a pair of point electrodes connected to and projecting therefrom into spark gap relation to each other, and an impedance in the connection between one of said point electrodes and one of said rst-named electrodes to control the discharge of the point electrodes.

NORMAN HENDRY. JOHN ANDREW LAIRD.

4rtarnrriciss CITED The following references are of record in the le of this patent: 

